1. Field of the Invention
This invention relates to hydraulic fluid control means and more specifically, relates to means for controlling speed and torque of an hydraulically actuated power means, such as power tongs employed in oil well drilling.
2. Description of the Prior Art
Power tongs rotating casing, tubing and pipe in connection with oil well drilling have been known in the art and manufactured in various forms by a number of manufacturers. In employing rotary power tongs and other hydraulic power means it is necessary to provide for a supply of hydraulic fluid at the desired pressure and velocity so as to produce the desired tong speed and torque. It is particularly important that effective controls be provided in a power tong in order to make sure that the proper tight joints are provided in drill string makeup while avoiding damage to the threads of the casings, tubes, pipes and couplings so to facilitate break-out of the threaded connections and reuse of the components.
It is also important that the hydraulic control system be such as to be dependable, economical to manufacture, easy to maintain and readily operable in a reliable fashion by the operator in the field.